Question:

What’s with Jews and food? For as long as I can remember, whenever we celebrate the yahrtzeit (anniversary of passing) of a family member, we always sponsor a breakfast after morning services—and sometimes we also sponsor a kiddush reception on the Shabbat prior. Why?

Response:

It appears that your family follows the chassidic custom of providing "tikkun" on the day of the yahrtzeit. "Tikkun"—which literally means “rectification”—is generally a light spread with some spirits, which the family of the deceased provides for the minyan-goers.

Why do we do it, and what exactly are we “fixing”? There are a number of explanations given:

  1. Chessed, kindness, is very potent. Giving people food is a great chessed and does wonders for the soul of the departed, in whose merit the food was given. Besides the gastronomical benefits, the tikkun provides a platform where people share each other’s company and uplifting Torah thoughts before they tackle another day. (In past generations, it was common to fast on the anniversary of passing. Now, mourners generally eat, but make up for it by making sure that others eat as well.)
  2. The people who partake of the food say blessings before and after they eat, and this brings merit for the soul.
  3. On the day of a relative’s yahrtzeit, one’s mazal, fortune, is diminished. However, when people raise a glass of whiskey and wish the mourner "L’chaim," "To life," or "Mazal tov,” these heartfelt blessings restore the mazal to its robust state. When toasting such a l’chaim, the customary Yiddish wish is “Di neshoma zol hobn an aliyah,” which means “The soul should have an ascent.”

Many have the custom to hold a festive meal, called a hillula, on the anniversary of passing of a righteous person. “Hillula” means “praise,” since we praise G‑d for the gift of a life well lived. This celebration of a complete, perfect life is similar to the siyum celebration held after completing a tractate of Talmud or another significant Torah accomplishment.


Source
Most of this information can be found in Nitei Gavrial, Laws of Mourning II 71, footnotes 1-4.